Method for producing difluoromethane and 1,1,1,2-tetrafluoroethane

ABSTRACT

According to the method for producing difluoromethane and 1,1,1,2-tetrafluoroethane, having the steps of: 
     (1) reacting methylene chloride and 1,1,2-trichloroethylene with hydrogen fluoride in a vapor phase In the presence of a fluorinating catalyst and 1,1,1,2-tetrafluoroethane in a first reactor; and 
     (2) reacting 1,1,1-trifluorochloroethane with hydrogen fluoride in a vapor phase in the presence of a fluorinating catalyst in a second reactor, and supplying the reaction mixture from the second reactor to the first reactor, HFC-32 can be obtained in high conversion and high selectivity by fluorinating HCC-30 using commonly a large (excess) amount of HF which is required for producing HFC-134a.

CROSS REFERNCE

This application is a 371 of PCT/IP94/02070 filed Dec. 09, 1994.

FIELD OF THE INVENTION

The present invention relates to a method for producing difluoromethaneand 1,1,1,2-tetrafluoroethane. Difluoromethane and1,1,1,2-tetrafluoroethane are alternative fluorocarbons, and are usefulas a cooling medium and the like.

DESCRIPTION OF RELATED ART

As the method for producing difluoromethane (CH₂ F₂, HFC-32), a liquidphase synthesis process (cf. U.S. Pat. No. 2,749,373) and vapor phasesynthesis process (cf. Japanese Patent Publication Nos. 3004/1967 and2251321/1984) comprising using methylene chloride (CH₂ Cl₂, HCC-30) as araw material are known.

It is a known fact that it is difficult to react methylene chloride ingood conversion according to the vapor phase synthesis process (cf."Chemistry and Industry of Fluorine Compound", page 267, published onDecember 1977 and Japanese Patent Publication No. 3004/1967). It ispossible to increase the conversion of methylene chloride by usingexcess HF relative to methylene chloride. However, a large amount of HFmust be disposed or recovered and, therefore, an economical disadvantagearises (cf. Japanese Patent Kokai Publication No. 2251321/1984).

Japanese Patent Kokai Publication No. 2942371/1991 discloses a processcomprising reacting 1,1,1-trifluorochloroethane (HCFC-133a) with HF toobtain 1,1,1,2-tetrafluoroethane (HFC-134a), adding1,1,2-trichloroethylene (HCC-1120) to a crude reaction gas to conductthe reaction from HCC-1120 into HCFC-133a in another reactor withoutexerting an influence on the other gas and recycling the formed 133a anda HF, as a process for producing efficiently 1,1,1-trifluorochloroethane(HCFC-133a) and 1,1,1,2-tetrafluoroethane (HFC-134a).

The conversion reaction from HCC-1120 into HCFC-133a is a largelyexothermic reaction, and it is suggested that the prevention of a heatspot formation in a catalyst layer by the reaction is useful to prolongthe catalytic life.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a method foreffectively and simultaneously producing difluoromethane and1,1,1,2-tetrafluoroethane in one apparatus.

The present invention provides a method for producing difluoromethaneand 1,1,1,2-tetrafluoroethane, comprising the steps of:

(1) reacting methylene chloride with hydrogen fluoride in a vapor phaseat a reaction temperature of 180° to 320° C. in the presence of afluorinating catalyst and 1,1,1,2-tetrafluoroethane to givedifluoromethane, and reacting 1,1,2-trichloroethylene with hydrogenfluoride to give 1,1,1-trifluorochloroethane, in a first reactor,

(2) reacting 1,1,1-trifluorochloroethane with hydrogen fluoride in avapor phase at a reaction temperature of 280° to 400° C., which ishigher than the reaction temperature of the first reactor, in thepresence of a fluorinating catalyst to give 1,1,1,2-tetrafluoroethane ina second reactor, and supplying the reaction mixture from the secondreactor to the first reactor;

(3) recovering difluoromethane, 1,1,1,2-tetrafluoroethane and hydrogenchloride from the reaction mixture of the first reactor; and

(4) supplying the remainder of the reaction mixture containing1,1,1-trifluorochloroethane from the first reactor to the second reactorafter recovering in the step (3).

In addition, the present invention provides a method for producingdifluoromethane and 1,1,1,2-tetrafluoroethane, comprising the steps of:

(1) reacting methylene chloride with hydrogen fluoride in a vapor phaseat a reaction temperature of 180° to 320° C. in the presence of afluorinating catalyst and 1,1,1,2-tetrafluoroethane to givedifluoromethane, and reacting 1,1,2-trichloroethylene with hydrogenfluoride to give 1,1,1-trifluorochloroethane, in a first reactor,

(2) reacting 1,1,1-trifluorochloroethane with hydrogen fluoride in avapor phase at a reaction temperature of 280° to 400° C. which is higherthan the reaction temperature of the first reactor in the presence of afluorinating catalyst to give 1,1,1,2-tetrafluoroethane in a secondreactor, and supplying the reaction mixture from the second reactor tothe first reactor;

(3) reacting the reaction mixture from the first reactor with hydrogenfluoride in a vapor phase at a reaction temperature of 150° to 240° C.,which is lower than the reaction temperature of the first reactor, inthe presence of a fluorinating catalyst to reduce an amount of methylenechloride existing in the reaction mixture, in a third reactor;

(4) recovering difluoromethane, 1,1,1,2-tetrafluoroethane and hydrogenchloride from the reaction mixture of the third reactor; and

(5) supplying the remainder of the reaction mixture containing1,1,1-trifluorochloroethane from the third reactor to the second reactorafter recovering in the step (4).

Further, the present invention provides a method for producingdifluoromethane and 1,1,1,2-tetrafluoroethane, comprising the steps of:

(1) reacting methylene chloride with hydrogen fluoride in a vapor phaseat a reaction temperature of 180° to 320° C. in the presence of afluorinating catalyst and 1,1,1,2-tetrafiuoroethane to givedifluoromethane, and reacting 1,1,2-trichloroethylene with hydrogenfluoride to give 1,1,1-trifluorochloroethane, in a first reactor;

(2) reacting 1,1,1-trifluorochloroethane with hydrogen fluoride in avapor phase at a reaction temperature of 280° to 400° C., which ishigher than the reaction temperature of the first reactor, in thepresence of a fluorinating catalyst to give 1,1,1,2-tetrafluoroethane ina second reactor, and supplying the reaction mixture from the secondreactor to the first reactor;

(3) reacting the reaction mixture from the first reactor with hydrogenfluoride in a vapor phase at a reaction temperature of 150° to 240° C.,which is lower than the reaction temperature of the first reactor, inthe presence of a fluorinating catalyst to reduce an amount of methylenechloride existing in the reaction mixture, in a third reactor;

(4) reacting the reaction mixture from the third reactor with hydrogenfluoride in a vapor phase at 100° to 190° C., which is lower than tereaction temperature of the third reactor, in the presence of afluorinating catalyst, in at least one fourth reactor;

(5) recovering difluoromethane, 1,1,1,2-tetrafluoroethane and hydrogenchloride from the reaction mixture from the fourth reactor; and

(6) supplying the remainder of the reaction mixture containing1,1,1-trifluorochloroethane from the fourth reactor to the secondreactor after recovering in the step (5).

The present invention further provides a method for producingdifluoromethane and 1,1,1,2-tetrafluoroethane, comprising the steps of:

(1) reacting methylene chloride with hydrogen fluoride in a vapor phaseat a reaction temperature of 180° to 320° C. in the presence of afluorinating catalyst and 1,1,1,2-tetrafluoroethane to givedifluoromethane, and reacting 1,1,2-trichloroethylene with hydrogenfluoride to give 1,1,1-trifluorochloroethane, in a first reactor;

(2) reacting 1,1,1-trifluorochloroethane with hydrogen fluoride in avapor phase at a reaction temperature of 280° to 400° C., which ishigher than the reaction temperature of the first reactor, in thepresence of a fluorinating catalyst to give 1,1,1,2-tetrafluoroethane ina second reactor, and supplying the reaction mixture from the secondreactor to the first reactor;

(3) recovering difluoromethane, 1,1,1,2-tetrafluoroethane and hydrogenchloride from the reaction mixture of the first reactor; and

(4) reacting the remainder of the reaction mixture containing1,1,1-trifluorochloroethane from the first reactor with hydrogenfluoride in a vapor phase at a temperature of 170° to 320° C. in thepresence of a fluorinating catalyst in a fifth reactor after recoveringin the step (3), and supplying the reaction mixture from the fifthreactor to the second reactor.

The present invention further provides a method for producingdifluoromethane and 1,1,1,2-tetrafluoroethane, comprising the steps of:

(1) reacting methylene chloride with hydrogen fluoride in a vapor phaseat a reaction temperature of 180° to 320° C. in the presence of afluorinating catalyst and 1,1,1,2-tetrafluoroethane to givedifluoromethane, and reacting 1,1,2-trichloroethylene with hydrogenfluoride to give 1,1,1,-trifluorochloroethane, in a first reactor;

(2) reacting 1,1,1-trifluorochloroethane with hydrogen fluoride in avapor phase at a reaction temperature of 280° to 400° C., which ishigher than the reaction temperature of the first reactor, in thepresence of a fluorinating catalyst to give 1,1,1,2-tetrafluoroethane ina second reactor, and supplying the reaction mixture from the secondreactor to the first reactor;

(3) reacting the reaction mixture from the first reactor with hydrogenfluoride in a vapor phase at 150° to 240° C., which is lower than thereaction temperature of the first reactor, in the presence of afluorinating catalyst to reduce an amount of methylene chloride existingin the reaction mixture, in a third reactor;

(4) recovering difluoromethane, 1,1,1,2-tetrafluoroethane and hydrogenchloride from the reaction mixture of the third reactor; and

(5) reacting the remainder of the reaction mixture containing1,1,1-trifluorochloroethane from the third reactor with hydrogenfluoride in a vapor phase at a temperature of 170° to 320° C. in thepresence of a fluorinating catalyst in a fifth reactor after recoveringin the step (4), and supplying the reaction mixture from the fifthreactor to the second reactor.

The present invention further provides a method for producingdifluoromethane and 1,1,1,2-tetrafluoroethane, comprising the steps of:

(1) reacting methylene chloride with hydrogen fluoride in a vapor phaseat a reaction temperature of 180° to 320° C. in the presence of afluorinating catalyst and 1,1,1,2-tetrafluoroethane to givedifluoromethane, and reacting 1,1,2-trichloroethylene with hydrogenfluoride to give 1,1,1-trifluorochloroethane, in a first reactor;

(2) reacting 1,1,1-trifluorochloroethane with hydrogen fluoride in avapor phase at a reaction temperature of 280° to 400° C., which ishigher than the reaction temperature of the first reactor, in thepresence of a fluorinating catalyst to give 1,1,1,2-tetrafluoroethane ina second reactor, and supplying the reaction mixture from the secondreactor to the first reactor;

(3) reacting the reaction mixture from the first reactor with hydrogenfluoride in a vapor phase at 150° to 240° C., which is lower than thereaction temperature of the first reactor, in the presence of afluorinating catalyst to reduce an amount of methylene chloride existingin the reaction mixture, in a third reactor;

(4) reacting the reaction mixture from the third reactor with hydrogenfluoride in a vapor phase at 100° to 190° C., which is lower than thereaction temperature of the third reactor, in the presence of afluorinating catalyst, in at least one fourth reactor;

(5) recovering difluoromethane, 1,1,1,2-tetrafluoroethane and hydrogenchloride from the reaction mixture of the fourth reactor; and

(6) reacting the remainder of the reaction mixture containing1,1,1-trifluorochoroethane from the fourth reactor with hydrogenfluoride in a vapor phase at a temperature of 170° to 320° C. in thepresence of a fluorinating catalyst in a fifth reactor after recoveringin the step (5), and supplying the reaction mixture from the fifthreactor to the second reactor.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic view illustrating an apparatus for conducting themethod of the present invention using first and second reactors.

FIG. 2 is a schematic view illustrating another embodiment of anapparatus for conducting the method of the present invention using firstand second reactors.

FIG. 3 is a schematic view illustrating an apparatus for conducting themethod of the present invention using first to third reactors.

FIG. 4 is a schematic view illustrating an apparatus for conducting themethod of the present invention using first to fourth reactors.

FIG. 5 is a schematic view illustrating an apparatus for conducting themethod of the present invention using first, second and fifth reactors.

FIG. 6 is a schematic view illustrating an apparatus for conducting themethod of the present invention using first to fifth reactors.

DETAILED DESCRIPTION OF THE INVENTION

In the present invention, it is preferred to recover the unreactedmethylene chloride (HCC-30) and/or chlorofluoromethane (HCFC-31, CH₂FCl) existing in the reaction mixture obtained from (a) the firstreactor when no third reactor exists, (b) the third reactor when thefirst and third reactors exist or (c) the fourth reactor when the first,third and fourth reactor exists, and to recycle the recovered HCC-30and/or HCFC-31 to the first or third reactor. These gases can berecovered from the reaction mixture by operations such as an extraction,a two phase separation, a fractional distillation, etc. When thereaction mixture is fed to the second reactor without recovering HCC-30and HCFC-31, the following reactions can arise in the second reactor.

HCC-30+2HF→HFC-32+2HCl

HCFC-31+HF→HFC-32+HCl

It is supposed that the resultant HCl decreases the conversion fromHCFC-133a into HFC-134a. However, a decrease in conversion becomes smallby decreasing the amount of the unreacted HCC-30 and HCFC-31 which arefed to the second reactor, so that the production efficiency of HFC-134ais increased.

The method of the present invention uses

(a) the first and second reactors,

(b) the first to third reactors,

(c) the first to fourth reactors,

(d) the first, second and fifth reactors,

(e) the first, second, third and fifth reactors, or

(f) the first to fifth reactors.

FIG. 1 is a schematic diagram illustrating an apparatus for conductingthe method of the present invention using first and second reactors.This apparatus has a first reactor 11, a second reactor 12, and aseparator 16 for recovering HFC-134a, HFC-32 and hydrogen chloride.

FIG. 2 is a schematic diagram illustrating another embodiment of anapparatus for conducting the method of the present invention using firstand second reactors. In this apparatus, the unreacted HCC-30 and/orHCFC-31 in the mixture obtained from the first reactor 11 are separated,and then the unreacted HCC-30 and/or HCFC-31 are supplied to the firstreactor 11.

FIG. 3 is a schematic diagram illustrating an apparatus for conductingthe method of the present invention using first to third reactors. Thisapparatus has a first reactor 21, a second reactor 22, a third reactor23, and a separator 26 for recovering HFC-134a, HFC-32 and hydrogenchloride.

FIG. 4 is a schematic diagram illustrating an apparatus for conductingthe method of the present invention using first to fourth reactors. Thisapparatus has a first reactor 31, a second reactor 32, a third reactor33, a fourth reactor 34, and a separator 36 for recovering HFC-134a,HFC-32 and hydrogen chloride.

FIG. 5 is a schematic diagram illustrating an apparatus for conductingthe method of the present invention using first, second and fifthreactors. This apparatus has a first reactor 41, a second reactor 42, afifth reactor 45 and a separator 46 for recovering HFC-134a, HFC-32 andhydrogen chloride.

FIG. 6 is a schematic diagram illustrating a apparatus for conductingthe method of the present invention using first to fifth reactors. Thisapparatus has a first reactor 101, a second reactor 102, a third reactor103, a fourth reactor 104, a fifth reactor 105, and a separator 106 forrecovering HFC-134a, HFC-32 and hydrogen chloride. It is also possibleto use an embodiment wherein no fourth reactor 104 exists.

In the first reactor, methylene chloride (HCC-30) is reacted withhydrogen fluoride in a vapor phase at a reaction temperature of 180° to320° C. in the presence of a fluorinating catalyst and1,1,1,2-tetrafluoroethane (HFC-134a) to give difluoromethane (HFC-32),and then 1,1,2-trichloroethylene (HCC-1120) is reacted with hydrogenfluoride to give 1,1,1-trifluorochloroethane (HCFC-133a). HFC-134a actsas a diluting agent for reducing a concentration of HCC-1120 andhydrogen fluoride.

In the first reactor, the following reactions arise.

    HCC-1120+3HF=HCFC-133a+2HCl+Δ29 kcal (exothermic)    (1)

    HCC-30+2HF=HFC-32+2HCl-Δ2 kcal (endothermic)         (2)

It is also possible that the following reaction arises.

    HFC-134a+HCl→HCFC-133a+HF                           (3)

HCl is generated according to the formula (1) and (2). It is supposedthat the generated HCl gives an adverse influence on HFC-134a formationbecause ΔG (Gibbs energy) of the reaction from HCFC-133a into HFC-134ais smaller than that of the formula (1). In the present invention,however, the actual conversion from HFC-134a into HCFC-133a is smallerthan an expected value derived from a relationship of the equilibriumconstant and the concentration of the raw material and the resultingsystem. Accordingly, it is possible to produce efficiently HCFC-133a andHCFC-32 without disadvantageous reaction from HFC-134a into HCFC-133a.The exothermic reaction (formula (1)) and the endothermic reaction(formula (2)) are combined and, therefore, the efficiency of energy isgood and it contributes to prevent the formation of heat spot in thereactor.

In the first reactor, HCFC-133a and HFC-32 can be produced efficiently.Since HFC-134a acts as a diluting agent for reducing the concentrationof HCC-1120 and HF which are the raw material, the control of thereaction heat becomes easier and more efficient. Similarly, an excessamount of HF reduces the concentration product of HCC-1120 and HF andacts as a heat remover and, therefore, the control of the reaction heatbecomes easy. In the first reactor, the amount of1,1-dichloro-2,2-difluoroethylene (CFC-1122) is also reduced(CFC-1122+HF→HCFC-133a).

Since the reaction (HCC-30+2HF→HFC-32+2HCl) in the first reactor canproceed in the presence of excess HF, the good conversion can beobtained. In this reaction, while the amount of HF may bestoichiometrically two equivalents, an excess amount of HF can givehigher conversion. In a system where a single reaction (the conversionfrom HCC-30) is conducted, there is a limitation of using the excessamount of HF in view of the cost of the apparatus. In a system whichalso include a reaction from HCC-1120, the stoichiometrically excessamount of HF is required in the second reactor, and the amount of HF canbe easily set to an excess amount so as to supply the reaction mixturefrom the second reactor to the first reactor. This is advantageous forsimultaneous production.

The reaction temperature of the first reactor is usually from 180° to320° C., preferably from 200° to 300° C., more preferably from 230° to270° C. When it is lower than 180° C., the conversion of HCC-1120 islowered. When it is higher than 320° C., the catalyst is remarkablydeteriorated and an amount of HFC-134a decreases. The contact time isusually from 0.5 to 60 seconds, preferably from 2 to 10 seconds. Thereaction pressure is not specifically limited unless the raw materialand product are liquefied. The reaction pressure is usually from 1 to 20atm, preferably from 1 to 10 atm, in view of simplification, economy,etc. In the first reactor, a fluorinating catalyst is usually used, butits type and production method are not specifically limited. Examples ofthe fluorinating catalyst include fluorinated chromium oxide obtained byfluorinating a heat-treated hydrate of chromium (III) hydroxide withhydrogen fluoride; chromium (III) trifluoride; fluorinated aluminumoxide obtained by fluorinating aluminum oxide with hydrogen fluoride;catalyst obtained by supporting at least one element selected from Ti,V, Zr, Mo, Ge, Sn and Pb on alumina, fluorinated alumina or partiallyfluorinated alumina; etc.

The raw material supplied to the first reactor may be HCC-1120, HCC-30and HF, and contains HFC-134a. It may also contain compounds such ashydrogen chloride (HCl), HCFC-133a, 1,1-dichloro-2,2-difluoroethylene(CFC-1122), etc.

In the raw material supplied to the first reactor, a molar ratio ofHCC-1120 to HCC-30 is not specifically limited, but is usually from 10:1to 1:2, preferably from 5:1 to 1:1. In the first reactor, the amount inmole of HF is usually from 1 to 50 times, preferably from 2 to 20 times,based on the total value of a 3-fold value of the mole amount of1,1,2-trichloroethylene and 2-fold value of mole amount of methylenechloride. The amount of HFC-134a is usually from 0.2 to 5 mol (e.g.about equimol) per 1 mol of HCC-1120.

In the second reactor, 1,1,1-trifluorochloroethane (HCFC-133a) isreacted with hydrogen fluoride in a vapor phase at a reactiontemperature of 280° to 400° C., which is higher than the reactiontemperature of the first reactor, in the presence of a fluorinatingcatalyst to produce 1,1,1,2-tetrafluoroethane (HFC-134a). The reactiontemperature is usually from 280° to 400° C., preferably from 290° to350° C. When the temperature is lower than 280° C., the amount of thegenerated HFC-134a is lowered. When the temperature is higher than 400°C., the deterfiFaion of the catalyst is remarkable. The temperature ofthe first reactor is set at a temperature lower than that of the secondreactor. For example, a difference between the temperatures of the firstand second reactors is from 30° to 120° C. The reaction pressure isusually from 1 to 20 atm, preferably from 1 to 10 atm. The contact timeis usually from 0.5 to 60 seconds, preferably from 2 to 10 seconds.Examples of the fluorinating catalyst are the same as those described inthe first reactor. The amount of hydrogen fluoride is usually from 0.9to 15 mol, preferably from 3 to 6 mol, based on 1 mol of HCFC-133a. Theraw material supplied to the second reactor contains HCFC-133a and HF,and it may contain trichloroethylene, HCFC-132b (CF₂ ClCHCl₂), HCFC-124(CF₃ CFHCl), etc.

In the third reactor, the reaction mixture obtained from the firstreactor is reacted with hydrogen fluoride in a vapor phase at 150° to240° C., which is lower than the reaction temperature of the firstreactor, in the presence of a fluorinating catalyst. In the thirdreactor, the unreacted HCC-30 existing in the first reactor is convertedinto HFC-32 so that the amount of HCC-30 is reduced. Furthermore, theresidual CFC-1122 is converted into HCFC-133a so that the amount ofCFC-1122 is reduced. HCC-30 may be introduced into the third reactorwithout introducing into the first reactor, because it is possible toset the reaction condition which is more suitable for the fluorinatingreaction of HCC-30 in the third reactor. The reaction temperature of thethird reactor is lower by usually from 30° to 170° C., preferably from50° to 120° C. than the reaction temperature of the first reactor. Thereaction pressure is usually from 1 to 20 atm, preferably from 1 to 10atm. The contact time is usually from 0.5 to 60 seconds, preferably from2 to 10 seconds. Examples of the fluorinating catalyst are the same asthose described in the first reactor. When the reaction temperature islower than 150° C., a size of the third reactor becomes large. On theother hand, when the reaction temperature is higher than 240° C.,CFC-1122 does not react sufficiently.

In a fourth reaction zone having at least one fourth reactor, thereaction mixture obtained from the third reactor is reacted withhydrogen fluoride in a vapor phase at 100° to 190° C., which is lowerthan the reaction temperature of the third reactor. The reactiontemperature of the fourth reactor is lower by usually from 20° to 140°C., preferably from 40° to 70° C., than that of the third reactor. Thereaction pressure is usually from 1 to 20 atm, preferably from 1 to 10atm. The contact time is usually from 0.5 to 60 seconds, preferably from2 to 10 seconds. When a plurality of fourth reactors exist in the fourthreaction zone, they are connected in a series, and a temperature of alast reactor in this zone which is far from the first reactor is lowerthan that of a leading reactor in this zone which is near the firstreactor. Examples of the fluorinating catalyst are the same as thosedescribed in the first reactor. In the fourth reactor, the residualCFC-1122 is converted into HCFC-133a so that the amount of CFC-1122 isreduced. A total volume of the reactor which is required for thereaction of removing CFC-1122 can be reduced by separating into twozones, i.e. third and fourth reactors, in comparison with the case ofone zone.

In the fifth reactor, the reaction mixture containing HCFC-133a isreacted with hydrogen fluoride in a vapor phase at a temperature of 170°to 320° C. The reaction temperature of the fifth reactor is usually from180° to 300° C., preferably from 190° to 280° C. The reaction pressureis usually from 1 to 20 atm, preferably from 1 to 10 atm. The contacttime is usually from 0.1 to 30 seconds, pfetefaly from 0.5 to 5 seconds.Examples of the fluorinating catalyst are the same as those described inthe first reactor. The presence of HCC-30 and HCC-1120 can give asignificant influence on the catalytic life in the second reactor and,therefore, the amount of HCC-30 and HCC-1120 can be decreased in thefifth reactor. Thereby, the catalytic life in the second reactor becomeslonger.

In the first to fifth reactors, as a contact system between the catalystand the raw material, both fluidized and fixed bed types can be used. Inaddition, a reactor having an insulating type or multi-tube type heatingsystem can be used. In the first reactor, a fixed bed multi-tube typereactor is preferable. The raw material supplied to the first to fifthreactors is preferably introduced into the reactor after previouslyconverting into a gas using an evaporator and the like.

In the method of the present invention, the raw material supplied fromthe exterior may be HCC-30, HCC-1120 and HF. The supply position ofHCC-30 and HCC-1120 supplied from the exterior is not specificallylimited. It is preferred to mix the raw material with the reactionmixture fed from the second reactor to the first reactor, or thereaction mixture fed from the first reactor to the third reactor whensupplying to the third reactor, because It is effective for the reactionto supply the raw material to the reactor in a state in which the rawmaterial is sufficiently preheated and mixed. As the premixing method,for example, there is a spray-mixing method comprising spraying a coldliquid and mixing it with a heat gas. The supply position of HF suppliedfrom the exterior is not specifically limited, but HF may be supplied ina step of recycling HCFC-133a and HF after removing HFC-32 and HFC-134a.It may also be supplied in several positions, e.g. before the firstreactor.

The reaction mixture obtained from the first, third or fourth reactorcontains HFC-32, HFC-134a and HCl, and further contain HF, HCFC-133a,HCC-1120, HCC-30, CFC-1122, CH₂ FCl (HCFC-31), CF₂ ClCH₂ Cl (HCFC-132b),etc. It is preferred to remove products (e.g. HFC-32, HFC-134a, HCl,etc.) from the system before feeding to the fifth reactor. The reasonwhy HCl is removed before feeding to the fifth reactor is that thefluorination of HCFC-133a in the fifth and second reactors is preventedby the presence of HCl. These gases can be separated and removed as anliquefied component by the cooling or the cooling under pressure. SinceHFC-32, HFC-134a and HCl are contained in the recovered substancewherein the product is removed, these are fed to a fractionaldistillation column and separated into the above product, the unreactedproduct and the intermediate raw material. In this case, a separationusing a two phase separation may be conducted.

The remainder of the reaction mixture wherein HFC-32, HFC-134a and HClare removed is optionally separated into a phase which is rich inHCFC-133a and HF and a phase which is rich in HCC-30 and HF by afractional distillation. It is preferred that the phase which is rich inHCFC-133a and HF is fed to the second reactor and the phase which isrich in HCC-30 and HF is fed to the first reactor so that they arereused.

PREFERRED EMBODIMENT OF THE INVENTION

The following Examples further illustrate the present invention.

COMPARATIVE EXAMPLE 1

The reaction was conducted using a reaction tube (A) (made of HastelloyC) having a double-tube type heating device and an inner diameter of 25mm, which was packed with 1500 g of a fluorinating catalyst (chromiumoxyfluoride), and a reaction tube (B) packed with 1500 g of afluorinating catalyst (chromium oxyfluoride).

1,1,1-Trifluorochloroethane (HCFC-133a) and HF in a flow rate (gas flowrate in a standard state, the same in the following) of 28 L/min and 112L/min, respectively, were introduced into the reaction tube (A) heatedto 320° C. and the reaction was conducted to generate1,1,1,2-tetrafluoroethane (HFC-134a). To the resultant gas,1,1,2-trichloroethylene (HCC-1120) was added in a flow rate of 4.48L/min and the reaction was conducted at 240° C. in the reaction tube (B)(made of Hastelloy C) having a double-tube type heating device and aninner diameter of 25 mm, which is packed with 1500 g of a fluorinatingcatalyst.

The gas evolved from the reaction tube (B) was subjected to GC analysisafter deacidificaton. As a result, the efflux rate of HFC-134a was 4.40L/min, and the conversion of HCC-1120 was 99.2%.

A heat spot at 255° C. was formed at the position which is about 30 cmaway from the inlet of an catalyst layer in the reaction tube (B).

Example 1

The same manner as in Comparative Example 1 was repeated except that1,1,2-trichloroethylene (HCC-1120) was mixed with methylene chloride(HCC-30) having a flow rate of 2.24 L/min and the mixture was introducedinto the reaction tube (B).

As a result of the GC analysis, the conversion of HCC-1120 was 98.9% andthe efflux rate of HFC-134a was 4.37 L/min. It has been found that theconversion of HCC-1120 and efflux rate of HFC-134a are almost the sameas those of Comparative Example 1.

Simultaneously HFC-32 was formed from HCC-30. As a result of thereaction, the conversion of HCC-30 was 92.0% and the selectivity ofHFC-32 was 94.4%.

EXAMPLE 2

The same manner as in Example 1 was repeated except that the gasgenerated in the reaction tube (B) was introduced into the reaction tube(C), which was packed with 1500 g of a fluorinating catalyst (chromiumoxyfluoride) and previously heated to 170° C.

As a result of the reaction at the outlet of the reactor (C), theconversion of HCC-30 was 92.1% and the selectivity of HFC-32 was 94.4%,based on the amount of HCC-30 introduced into the reaction tube (B).

At the outlet of the reaction tube (B), CFC-1122 existed in an amount ofabout 500 ppm based on HFC-134a, but the amount thereof was deceased to15 ppm at the outlet of the reaction tube (C).

Comparative Example 2

The same manner as in Comparative Example 1 was repeated except that thereaction was conducted by adding 1,1,2-trichloroethylene and methylenechloride in a flow rate of 0.1 L/min and 0.2 L/min, respectively, to aninlet gas of the reaction tube (A).

The efflux rate of HFC-134a from the reaction tube (A) was 4.46 L/min atthe beginning of the reaction, but was gradually decreased to 3.35 L/minafter 300 hours.

EXAMPLE 3

The same manner as in Comparative Example 2 was repeated except that,after eaeting the above gas In the reaton tube (C) heated previously to300° C. in which 300 g of a fluorinating catalyst was charged, thereaction gas was further introduced into the reaction tubes (A) and (B)and then reacted.

The gas evolved from the reaction tube (A) was subjected to GC analysisafter deacidification. As a result, the efflux rate of HFC-134a from thereaction tube (A) was 4.50 L/min at the beginning of the reaction, andwas 4.08 L/min even after 300 hours.

At this time, methylene chloride was hardly detected at the outlet ofthe reaction tube (C).

EFFECT OF THE INVENTION

The effects of the present invention are as follows.

HCl is generated in the first reactor, and it is supposed that thegenerated HCl gives a deleterious influence on HFC-134a. In the presentinvention, however, the practical conversion from HFC-134a intoHCFC-133a is smaller than an expected value derived from a relationshipof the equilibrium constant and the concentration of the raw materialand the generated system. Accordingly, it is possible to produceHCFC-133a and HFC-32 efficiently without causing disadvantageousconversion from HFC-134a into HCFC-133a. The efficiency of energy isgood and the formation of a heat spot in the reactor is inhibited.

In the present invention, HCFC-134a and HFC-32 can be producedefficiently. When HFC-134a is used as a diluting agent and excess HF issupplied, HF acts as a heat remover and, therefore, the control of thereaction heat becomes easier and more efficient. In the first reactor,the amount of 1,1-dichloro-2,2-difluoroethylene (CFC-1122) is alsoreduced.

It as possible to proceed the reaction in the first reactor in thepresence of excess HF without causing a problem on the cost of theapparatus and, therefore, the reaction (HCC-30+2HF→HFC-32+2HCl) proceedsin good conversion.

According to the present invention, it is possible to give HFC-32 andHFC-134a in good yield without causing a deleterious Influence such asthe decrease in conversion of HCC-1120, the decease in amount ofHFC-134a, etc.

What is claimed is:
 1. A method for producing difluoromethane and1,1,1,2-tetrafluoroethane, comprising the steps of:(1) reactingmethylene chloride with hydrogen fluoride in a vapor phase at a reactiontemperature of 180° to 320° C. in the presence of a fluorinatingcatalyst and 1,1,1,2-tetrafluoroethane to give difluoromethane, andreacting 1,1,2-trichloroethylene with hydrogen fluoride to give1,1,1-trifluorochloroethane, in a first reactor; (2) reacting1,1,1-trifluorochloroethane with hydrogen fluoride in a vapor phase at areaction temperature of 280° to 400° C., which is higher than thereaction temperature of the first reactor, in the presence of afluorinating catalyst to give 1,1,1,2-tetrafluoroethane in a secondreactor, and supplying the reaction mixture from the second reactor tothe first reactor; (3) recovering difluoromethane,1,1,1,2-tetrafluoroethane and hydrogen chloride from the reactionmixture of the first reactor; and (4) supplying the remainder of thereaction mixture containing 1,1,1-trifluorochloroethane from the firstreactor to the second reactor after recovering in the step (3), whereinsaid fluorinating catalyst is selected from: (i) fluorinated chromiumoxide obtained by fluorinating a heat-treated hydrate of chromium (III)with hydrogen fluoride, (ii) chromium (III) trifluoride, (iii)fluorinated aluminum oxide obtained by fluorinating aluminum oxide withhydrogen fluoride, and (iv) a catalyst obtained by supporting oneelement selected from Ti, V, Zr, Mo, Ge, Sn and Pb on alumina,fluorinated alumina or partially fluorinated alumina.
 2. The methodaccording to claim 1, wherein methylene chloride and/orchlorofluoromethane existing in the reaction mixture obtained from thefirst reactor are recovered, and then the recovered methylene chlorideand/or chlorofluoromethane are supplied to the first reactor.
 3. Amethod for producing difluoromethane and 1,1,1,2-tetrafluoroethane,comprising the steps of:(1) reacting methylene chloride with hydrogenfluoride in a vapor phase at a reaction temperature of 180° to 320° C.in the presence of a fluorinating catalyst and 1,1,1,2-tetrafluoroethaneto give difluoromethane, and reacting 1,1,2-trichloroethylene withhydrogen fluoride to give 1,1,1-trifluorochloroethane, in a firstreactor; (2) reacting 1,1,1-trifluorochloroethane with hydrogen fluoridein a vapor phase at a reaction temperature of 280° to 400° C. in thepresence of a fluorinating catalyst to give 1,1,1,2-tetrafluoroethane ina second reactor, and supplying the reaction mixture from the secondreactor to the first reactor; (3) reacting the reaction mixture from thefirst reactor with hydrogen fluoride in a vapor phase at a reactiontemperature of 150° to 240° C., which is lower than the reactiontemperature of the first reactor, in the presence of a fluorinatingcatalyst to reduce an amount of methylene chloride existing in thereaction mixture, in a third reactor; (4) recovering difluoromethane,1,1,1,2-tetrafluoroethane and hydrogen chloride from the reactionmixture of the third reactor; and (5) supplying the remainder of thereaction mixture containing 1,1,1-trifluorochloroethane from the thirdreactor to the second reactor after recovering in the step (4), whereinsaid fluorinating catalyst is selected from: (i) fluorinated chromiumoxide obtained by fluorinating a heat-treated hydrate of chromium (III)with hydrogen fluoride, (ii) chromium (III) trifluoride, (iii)fluorinated aluminum oxide obtained by fluorinating aluminum oxide withhydrogen fluoride, and (iv) a catalyst obtained by supporting oneelement selected from Ti, V, Zr, Mo, Ge, Sn and Pb on alumina,fluorinated alumina or partially fluorinated alumina.
 4. The methodaccording to claim 3, wherein methylene chloride and/orchlorofluoromethane existing in the reaction mixture obtained from thethird reactor are recovered, and then the recovered methylene chlorideand/or chlorofluorormethane are supplied to the first reactor or thirdreactor.
 5. A method for producing difluoromethane and1,1,1,2-tetrafluoroethane, comprising the steps of:(1) reactingmethylene chloride with hydrogen fluoride in a vapor phase at a reactiontemperature of 180° to 320° C. in the presence of a fluorinatingcatalyst and 1,1,1,2-tetrafluoroethane to give difluoromethane, andreacting 1,1,2-trichloroethylene with hydrogen fluoride to give1,1,1-trifluorochloroethane, in a first reactor; (2) reacting1,1,1-trifluorochloroethane with hydrogen fluoride in a vapor phase at areaction temperature of 280° to 400° C., which is higher than thereaction temperature of the first reactor, in the presence of afluorinating catalyst to give 1,1,1,2-tetrafluoroethane in a secondreactor, and supplying the reaction mixture from the second reactor tothe first reactor; (3) reacting the reaction mixture from the firstreactor with hydrogen fluoride in a vapor phase at a reactiontemperature of 150° to 240° C., which is lower than the reactiontemperature of the first reactor, in the presence of a fluorinatingcatalyst to reduce an amount of methylene chloride existing in thereaction mixture, in a third reactor; (4) reacting the reaction mixturefrom the third reactor with hydrogen fluoride in a vapor phase at 100°to 190° C., which is lower than the reaction temperature of the thirdreactor, in the presence of a fluorinating catalyst, in at least onefourth reactor; (5) recovering difluormethane, 1,1,1,2-tetrafluoroethaneand hydrogen chloride from the reaction mixture of the fourth reactor;and (6) supplying the remainder of the reaction mixture containing1,1,1-trifluorochloroethane from the fourth reactor to the secondreactor after recovering in the step (5), wherein said fluorinatingcatalyst is selected from: (i) fluorinated chromium oxide obtained byfluorinating a heat-treated hydrate of chromium (III) with hydrogenfluoride, (ii) chromium (III) trifluoride, (iii) fluorinated aluminumoxide obtained by fluorinating aluminum oxide with hydrogen fluoride,and (iv) a catalyst obtained by supporting one element selected from Ti,V, Zr, Mo, Ge, Sn and Pb on alumina, fluorinated alumina or partiallyfluorinated alumina.
 6. The method according to claim 5, whereinmethylene chloride and/or chlorofluoromethane existing in the reactionmixture obtained from the fourth reactor are recovered, and then therecovered methylene chloride and/or chlorofluoromethane are supplied tothe first reactor or third reactor.
 7. A method for producingdifluoromethane and 1,1,1,2-tetrafluoroethane, comprising the stepsof:(1) reacting methylene chloride with hydrogen fluoride in a vaporphase at a reaction temperature of 180° to 320° C. in the presence of afluorinating catalyst and 1,1,1,2-tetrafluoroethane to givedifluoromethane, and reacting 1,1,2-trichloroethylene with hydrogenfluoride to give 1,1,1-trifluorochloroethane, in a first reactor; (2)reacting 1,1,1-trifluorochloroethane with hydrogen fluoride in a vaporphase at a reaction temperature of 280° to 400° C., which is higher thanthe reaction temperature of the first reactor, in the presence of afluorinating catalyst to give 1,1,1,2-tetrafluoroethane in a secondreactor, and supplying the reaction mixture from the second reactor tothe first reactor; (3) recovering difluoromethane,1,1,1,2-tetrafluoroethane and hydrogen chloride from the reactionmixture of the first reactor; and (4) reacting the remainder of thereaction mixture containing 1,1,1-trifluorochloroethane from the firstreactor with hydrogen fluoride in a vapor phase at a temperature of 170°to 320° C. in the presence of a fluorinating catalyst in a fifth reactorafter recovering in the step (3), and supplying the reaction mixturefrom the fifth reactor to the second reactor, wherein said fluorinatingcatalyst is selected from: (i) fluorinated chromium oxide obtained byfluorinating a heat-treated hydrate of chromium (III) with hydrogenfluoride, (ii) chromium (III) trifluoride, (iii) fluorinated aluminumoxide obtained by fluorinating aluminum oxide with hydrogen fluoride,and (iv) a catalyst obtained by supporting one element selected from Ti,V, Zr, Mo, Ge, Sn and Pb on alumina, fluorinated alumina or partiallyfluorinated alumina.
 8. A method for producing difluoromethane and1,1,1,2-tetrafluoroethane, comprising the steps of:(1) reactingmethylene chloride with hydrogen fluoride in a vapor phase at a reactiontemperature of 180° to 320° C. in the presence of a fluorinatingcatalyst and 1,1,1,2-tetrafluoroethane to give difluoromethane, andreacting 1,1,2-trichloroethylene with hydrogen fluoride to give1,1,1-trifluorochloroethane, in a first reactor; (2) reacting1,1,1-trifluorochloroethane with hydrogen fluoride in a vapor phase at areaction temperature of 280° to 400° C., which is higher than thereaction temperature of the first reactor, in the presence of afluorinating catalyst to give 1,1,1,2-tetrafluoroethane in a secondreactor, and supplying the reaction mixture from the second reactor tothe first reactor; (3) reacting the reaction mixture from the firstreactor with hydrogen fluoride in a vapor phase at 150° to 240° C.,which is lower than the reaction temperature of the first reactor, inthe presence of a fluorinating catalyst to reduce an amount of methylenechloride existing in the reaction mixture, in a third reactor; (4)recovering difluormethane, 1,1,1,2-tetrafluoroethane and hydrogenchloride from the reaction mixture of the first reactor; and (5)reacting the remainder of the reaction mixture containing1,1,1-trifluorochloroethane from the third reactor with hydrogenfluoride in a vapor phase at a temperature of 170° to 320° C. in thepresence of a fluorinating catalyst in a fifth reactor after recoveringin the step (4), and supplying the reaction mixture from the fifthreactor to the second reactor, wherein said fluorinating catalyst isselected from: (i) fluorinated chromium oxide obtained by fluorinating aheat-treated hydrate of chromium (III) with hydrogen fluoride, (ii)chromium (III) trifluoride, (iii) fluorinated aluminum oxide obtained byfluorinating aluminum oxide with hydrogen fluoride, and (iv) a catalystobtained by supporting one element selected from Ti, V, Zr, Mo, Ge, Snand Pb on alumina, fluorinated alumina or partially fluorinated alumina.9. A method for producing difluoromethane and 1,1,1,2-tetrafluoroethane,comprising the steps of:(1) reacting methylene chloride with hydrogenfluoride in a vapor phase at a reaction temperature of 180° to 320° C.in the presence of a fluorinating catalyst and 1,1,1,2-tetrafluoroethaneto give difluoromethane, and reacting 1,1,2-trichloroethylene withhydrogen fluoride to give 1,1,1-trifluorochloroethane, in a firstreactor; (2) reacting 1,1,1-trifluorochloroethane with hydrogen fluoridein a vapor phase at a reaction temperature of 280° to 400° C., which ishigher than the reaction temperature of the first reactor, in thepresence of a fluorinating catalyst to give 1,1,1,2-tetrafluoroethane ina second reactor, and supplying the resulting reaction mixture from thesecond reactor to the first reactor; (3) reacting the reaction mixturefrom the first reactor with hydrogen fluoride in a vapor phase at 150°to 240° C., which is lower than the reaction temperature of the firstreactor, in the presence of a fluorinating catalyst to reduce an amountof methylene chloride existing in the reaction mixture, in a thirdreactor; (4) reacting the reaction mixture from the third reactor withhydrogen fluoride in a vapor phase at 100° to 190° C., which is lowerthan the reaction temperature of the third reactor, in the presence of afluorinating catalyst, in at least one fourth reactor; (5) recoveringdifluoromethane, 1,1,1,2-tetrafluoroethane and hydrogen chloride fromthe reaction mixture of the fourth reactor; and (6) reacting theremainder of the reaction mixture containing 1,1,1-trifluorochloroethanefrom the fourth reactor with hydrogen fluoride in a vapor phase at atemperature of 170° to 320° C. in the presence of a fluorinatingcatalyst in a fifth reactor after recovering in the step (5), andsupplying the reaction mixture from the fifth reactor to the secondreactor; wherein said fluorinating catalyst is selected from: (i)fluorinated chromium oxide obtained by fluorinating a heat-treatedhydrate of chromium (III) with hydrogen fluoride, (ii) chromium (III)trifluoride, (iii) fluorinated aluminum oxide obtained by fluorinatingaluminum oxide with hydrogen fluoride, and (iv) a catalyst obtained bysupporting one element selected from Ti, V, Zr, Mo, Ge, Sn and Pb onalumina, fluorinated alumina or partially fluorinated alumina.
 10. Themethod according to claim 3, 5, 8 or 9, wherein methylene chloride isreacted with hydrogen fluoride in the third reactor instead of the firstreactor.
 11. The method according to claim 3, wherein methylene chlorideis reacted with hydrogen fluoride in the third reactor instead of thefirst reactor, and methylene chloride and/or chlorofluoromethaneexisting in the reaction mixture obtained from the third reactor arerecovered, and then the recovered methylene chloride and/orchlorofluoromethane are supplied to the third reactor.
 12. The methodaccording to claim 5, wherein methylene chloride is reacted withhydrogen fluoride in the third reactor instead of the first reactor, andmethylene chloride andlor chlorofluoromethane existing in the reactionmixture obtained from the fourth reactor are recovered, and then therecovered methylene chloride and/or chlorofluoromethane are supplied tothe third reactor.
 13. The method according to claim 1, wherein a moleamount of hydrogen fluoride in the first reactor is from 1 to 50 times,based on the total value of a 3-fold value of the mole amount of1,1,2-trichloroethylene and 2-fold value of mole amount of methylenechloride.
 14. The method according to any claim 1, wherein a mole amountof hydrogen fluoride in the first reactor is from 10 to 20 times, basedon the total value of a 3-fold value of the mole amount of1,1,2-trichloroethylene and 2-fold value of mole amount of methylenechloride.